The present invention relates to a novel triacylglycerol incorporating an antioxidant moiety and lipid compositions comprising triacylglycerols including antioxidant moieties and unsaturated fatty acids.
Fatty acids are saturated or unsaturated aliphatic monocarboxylic acids, usually with an even number of carbon atoms that occur naturally in the form of glycerides in fats and fatty oils, waxes and essential oils. Saturated fatty acids have the general formula, CnH(2n+1)COOH. Hydroxy-fatty acids such as ricinoleic acid are also known to be present naturally in certain oils. All fatty acids are carboxylic acids, which is a broad term that encompasses any compound with a carboxylic group, COOH. Fatty acids are numbered from the carboxylic carbon atom. The position of double bonds is indicated by the Greek letter delta (δ) followed by the carbon number of the double bond, i.e., C 20:5 omega-3 δ 5,8,11,14,17. The omega (ω) notation refers to the position of a double bond as an indicated number of carbon atoms from the non-carboxy terminal end of an unsaturated fatty acid. The designation for eicosapentaenoic acid, an omega-3 polyunsaturated fatty acid, is C 20:5 ω-3 δ 5,8,11,14,17. Docosapentaenoic acid is C 22:5 ω-3 δ 7,10,13,16,19 and docosahexaenoic acid (DHA) is C 22:6 ω-3 δ 7,10,13,16,19. The designation omega-6 (ω-6) refers to a fatty acid such as linoleic acid that has a double bond which is at carbon position six from the non-carboxy terminal end of the fatty acid.
The ω-3 fatty acids are essential for maintenance of health and prevention of disease. As noted above, DHA is a ω-3 fatty acid having 22 carbon atoms and three double bonds. It is the major component of insulation tissue for the retinal photoreceptors. It plays a major role in the [1]: • Maintenance of cell membrane fluidity in brain and eyes • Reduction of intraocular pressure • Constant renewal of retinal components after oxidative damage • Reduction of clogging/hardening of arteries • Enhancement of visual acuity Thus, a supply of DHA, would be useful in preventing vision disorders such as age-related macular degeneration and glaucoma through the reduction of arterial plaque and intraocular pressure. In fact, the ω-3 fatty acids cause a lowering of blood pressure throughout the body's arterial network, reduction in cholesterol levels, as well as vasodilation resulting in the alleviation of coronary heart disease.
The ω-3 fatty acids also act as anti-inflammatory agents, making them beneficial for patients with rheumatoid arthritis and other inflammatory ailments. These acids also protect myelin, which shields the nerves, and may be useful in treating or ameliorating a variety of neural disorders such as dementia or depression. These fatty acids may also be helpful in preventing cancer. However, due to their high unsaturation, they are quite unstable and subject to oxidation at the ω-3 double bond.
DHA can be supplied to the body either as dietary DHA or in precursor form as alpha-linolenic acid (ALA), also from a dietary source. Dietary DHA originates mainly from fish oils with the associated drawbacks such as the fishy odor and possible mercury contamination. However, findings from animal studies suggest that brain cells may prefer to make DHA from its precursor, ALA, rather than absorb it pre-formed [2].
ALA is obtained from plant seed oils such as oils from flaxseed, perilla, hemp, canola or soybean and is relatively odor-free. A comparison between the properties of ALA and DHA indicates that ALA supplementation is also superior to that of DHA as a result of many different factors such as:                1. Price: Cost of dietary DHA supplementation even without extraction and processing from fish oil is very high.        2. Absorption: The pancreatic lipase activity towards fatty acids decreases with chain length. Consequently, DHA is not as well accepted as substrate and is released more slowly from triacylglycerols as compared to ALA.        3. Both achieve similar effects: ALA can be converted to DHA to the extent required by the body even in preterm infants. The brain/retina also has a capability for the conversion.        4. Stability: ALA with its three double bonds is less prone to oxidative damage than DHA with its six double bonds.        5. Concentration: The nervous system is not protected against a large excess of DHA, which could increase n−3/n−6 ratio and could lead to abnormal function, and which might be difficult to reverse. This DHA excess is avoidable by supplying the precursor, ALA, which will be converted to DHA as required by the body.        
Consequently, it may be preferable to supply DHA through its precursor, ALA, in nutraceutical compositions and products.
It is known that mitochondrial and peroxisomal fatty oxidation rates increase with increasing dietary levels of ALA. The activity of enzymes such as carnitine palmitoyltransferase, acyl-CoA oxidase, 3-ketoacyl-CoA thiolase, and 2,4-dienoyl-CoA reductase is enhanced. Smaller but significant increases by ALA of the activity of acyl-CoA dehydrogenase, enoyl-CoA hydratase, and delta 3, delta 2-enoyl-CoA isomerase have also been observed. However, dietary ALA was reported to greatly reduce the activities of some enzymes such as 3-hydroxy-acyl-CoA dehydrogenase and pyruvate kinase. Therefore, while β-oxidation of fatty acids is higher for unsaturated fats, the activity of pyruvate kinase (which converts glucose catabolite, phosphoenol pyruvate into pyruvate) an important enzyme in the glycolysis pathway is reduced, implying lesser energy. An exogenous supply of pyruvic acid will also enable further stimulation of the fatty acid anabolic pathways to convert them into their more unsaturated counterparts rather than their channeling towards β-oxidation.
Hence, it may be beneficial to supplement ALA with pyruvic acid to offset this effect. Pyruvic acid is a three-carbon alpha-keto acid with relatively strong antioxidative activity and may enhance the stability of ALA when combined in a formulation. However, pyruvic acid is a strong, unstable ketoacid, which cannot be administered orally or parenterally. Salts of pyruvic acid are also not physiologically suitable. Amino-compounds containing pyruvate such as pyruvylglycine lead to excessive nitrogen loads. Also, flooding plasma with glycine may interfere with the transport of some amino acids across the blood-brain barrier. Accordingly, these pyruvate compounds are less suited to treating an organ in vivo, and it is recognized that a need exists to provide a pyruvate delivery compound that is more physiologically acceptable [3].
One such potential compound is a pyruvylglycerol. This would be more stable and pH-neutral. The acylglycerol will be hydrolyzed to pyruvic acid by non-specific esterases present in plasma, tissues and the gastrointestinal tract as well as gastric and pancreatic lipases, and subsequently neutralized by the body's buffers.
Apart from the benefits of alpha-keto acids described above, they also confer other health benefits particularly due to their antioxidant capacity. This is possible because they can act as scavengers of free radicals and can also prevent lipid peroxidation by inhibiting formation of free radicals. This ensures their usefulness in prevention and treatment of disorders related to aging (such as cataract and glaucoma), diabetes, calcium overexcretion (as in osteoporosis) and cancers.
Structured lipids consisting of fatty acids esterified to the glyceryl backbone are known in the art. Structured triacylglycerols, in contrast to natural triacylglycerols, can be classified as any oil and fat modified or synthesized by any artificial means, such as hydrogenation, fractionation, blending, interesterification, esterification, and even from bioengineered plants. However, the common definition of structured triacylglycerols refers to those oils and fats containing polyunsaturated fatty acids and medium- or short-chain fatty acids, or those in which different fatty acids are specifically located in the glycerol backbone.
Most structured lipids have involved the interesterification of oils to rearrange the fatty acid distribution, to enhance either the content of PUFA or that of the medium-chain (MCFA—number of carbons=8, 10, 12) or short-chain fatty acids (SCFA—number of carbons=3, 4, 6). MCFA and SCFA are excellent sources of ready energy for the body due to their rapid absorption and are preferred because they have a low caloric value. Structured lipids containing MCFA are well known and their synthesis and composition have been widely reported [4-16].
Commercially available structured triacylglycerols include Salatrim™ (Benefat™ containing acetic, propionic, butyric and stearic acids esterified to glycerol) from Cultor Food Science and Nabisco Inc., Caprenin™ (caprocaprylobehenin, containing caprylic, capric and behenic acids esterified to glycerol) from Procter & Gamble, Captex™ from Abitec Corp., Neobee™ from Stepan Company, Impact™ from Novartis Nutrition, and Structolipid™ from Fresenius Kabi. Enzymatic interesterification with sn-1,3 specific lipases has also been used by industry for the production of structured lipids usable as cocoa butter substitutes [17-20].
Although the prior art shows that there has been relatively high degree of activity in designing triglycerides [21-36] for certain nutritional and medical uses, there is no teaching in any of the prior art, which refers to combining antioxidant short chain alpha-keto carboxylic acids with long-chain unsaturated fatty acids.
Pyruvate compounds such as pyruvate thiolester, glycerol-pyruvate ester or a dihydoxyacetone-pyruvate ester have been synthesized [37-39]. The glycerol-pyruvate esters synthesized were pyruvyl-diacetyl-glycerol and dipyruvyl-acetyl-glycerol. These were prepared by esterification of diacetin and monoacetin, respectively, with pyruvyl chloride. It appears that these are the only glyceryl pyruvate compounds reported in literature, whereby pyruvic acid is coesterified with a short-chain fatty acid such as acetic acid.
However, there is no suggestion or disclosure of a triacylglycerol or an oil containing pyruvic or other α-keto acids with widespread health benefits, and hence, for use as a nutraceutical or functional food bioactive.
Therefore, there is a need in the art for lipid composition, which includes triacylglycerols comprising an antioxidant moiety and nutritionally beneficial fatty acids and methods for forming such a lipid composition with relatively high yields.